A choice-based story presents a scene and then a short list of things you can do or say. You tap one, the story continues. It is the dominant format in story apps because it is quick to read on a phone and simple to charge for.
Free choices and premium choices
Most apps mark some options with a currency icon: diamonds, gems, keys, tickets, hearts. Those are premium choices, and they typically buy the more dramatic version of a scene, an outfit, or a romance path. The free option always exists, so a story can be finished without paying, but the version you get is the plainer one.
This is the format's central tension. The choice that looks most interesting is the one with a price on it, and the decision arrives in the middle of a scene rather than at a checkout.
Energy, keys and waiting
Alongside choices, most apps meter how much you can read at once. You get a number of chapters, then wait for a timer to refill, or pay to skip it. Some apps let a subscription remove the timer altogether, which is usually the cheaper route for anyone reading daily.
How much do choices change
Less than the interface implies, usually. Most choice-based stories loop back to a shared next chapter, so the choice colours the scene rather than redirecting the plot. Endings are the honest measure: where an app publishes how many a story has, that number tells you more than any promise about branching.
Before you start a long one
Three things are worth knowing in advance: how many chapters the story has, what a premium choice costs in real money once the currency is converted, and whether a subscription exists that covers the timer. All three are findable before chapter one, and none of them is shown to you at the moment you are asked to pay.
See also branching story, interactive fiction and the glossary.